WordPress MU

are there custom fields that the admin sets up for each blog?

and if so how can i theme them as well as the output?

custom fields for what kind of information exactly?

Pretend I don't know what cck is for drupal.

lets say i would like to add a input field for a thumbnail for the article.

or a teaser....and i need as requirement for each post

You would have to write a plugin for that. See the codex for info on writing plugins.

"would like to add a input field for a thumbnail for the article"

Check out any of the magazine themes. many of them do this. It;s just adding a custom field for the thumbnail.

Or, there's a plugin called "get the image" which will auto-pull the first image in a post and display it as a thumbnail.

"or a teaser...."

Built in already. Use the excerpt.

"and i need as requirement for each post"

That's the sticky part. The only requirement for a post in WP is content.